ingridscience

Collect oxygen over water.
Relight a glowing splint by lowering it into the tube of oxygen. Feel the exothermic reaction.

Collect CO2 over water - puts out a lighted splint.

This activity investigates the chemistry of oxygen laundry bleach (show bottle). We'll look at a chemical reaction it undergoes, why it is environmentally safe, and the many ways that hydrogen peroxide is used in our world.

Hydrogen peroxide chemical reaction
Show the hydrogen peroxide molecule, H2O2. Tell students that molecule breaks down into water and a gas. Tell students they will figure out what this gas is.
Ask students to build two H2O2 molecules. Then tell them that as these break apart they will make two new molecules, one of which is water. Ask students to break apart the hydrogen peroxide molecules and use the atoms and bonds to build two water molecules (two H2O). They should then use all the remaining atoms and bonds, and fill all the holes in the atoms, to build the other molecule that is made in the chemical reaction.
They should make O2.
Hence the chemical reaction when hydrogen peroxide breaks apart is 2H2O2 -> 2H2O + O2.

Oxygen laundry bleach is environmentally safe because as it works, it breaks into only oxygen and water, which are in living things already. Whereas chlorine bleach (regular bleach) breaks down into molecules with chlorine in them, which are harmful to the environment. Oxygen bleach does not bleach coloured clothes to white if it is spilled on them, but it does remove dirt from clothes.

The chemical reaction happens on its own slowly in the bottle of hydrogen peroxide, but is sped up by other materials.

Hydrogen peroxide making bubbles with different materials
Hydrogen peroxide slowly breaks down on it’s own, but this decomposition is massively speed up with certain materials, called a catalyst.
Students will test different materials for speeding up H2O2 decomposition. Discuss how, if the materials breaks hydrogen peroxide down, they will see oxygen gas forming, as bubbles.

Set up a table of materials that students can gather in their tray to test. Also provide them with magnifiers so that they can look up close for bubbling. A range of materials that do and don't make bubbles is ideal:
yeast (lots of bubbles)
soil or potato (many bubbles)
pieces of dirty cloth smeared with potato juice and soil (some bubbles)
tissue or plastic bag or pieces of cloth (no bubbles).
Set up tables where students can add hydrogen peroxide to their materials, to look for bubbles, and where they can rinse their trays once they have used all the wells.
Hand out a tray and worksheet to each student.
Once students have used all the provided materials, they can look for more materials around the classroom to test:
pencil or eraser shavings, hair, moss or rocks from outside, dip their own finger in hydrogen peroxide.

Discussion:
Collect students results on the board.
Ask students to figure out a pattern of what breaks down hydrogen peroxide and what does not. Help them arrive at living things produce more bubbles and non-living things do not (hair is not living, but is a dead protein strand exuded by a living cell in the scalp).

Living things contain catalase, a molecule (an enzyme) that breaks down hydrogen peroxide into oxygen and water.
The reason living things contain catalase is because living things produce hydrogen peroxide naturally all the time, through the chemical reactions happening in them. But hydrogen peroxide can be damaging to cells as it degrades into radicals before becoming the harmless oxygen and water. The radicals can attack DNA and proteins and membrane lipids, to kill cells. The catalase quickly converts hydrogen peroxide to oxygen and water, so the radicals do not hang around for too long to do damage.
Hence anything with living cells in it bubbles with H2O2.

Hydrogen peroxide uses in our world

The bombardier beetle uses hydrogen peroxide to make a hot irritating liquid that it squirts at predators.
In separate chambers in its abdomen, the beetle stores H2O2 and catalase enzyme, as well as a quinone molecule. On demand, it mixes the hydrogen peroxide and catalase to make pressurized oxygen and water hot gases. Hydroxyquinone is also catalysed to quinone, an irritant. The mixture of hot gases and liquid are ejected at the intruder.

Propellant in rockets and torpedoes.
Hydrogen peroxide can be catalysed to gaseous oxygen and water, to be used as a propellant.
Silver or platinum are catalysts which drive the reaction.
82% H2O2 used on Russian Soyuz rocket to drive the turbopumps on the boosters. https://en.wikipedia.org/wiki/High-test_peroxide#Applications

Antiseptic: hydrogen peroxide is toxic to cells, as the radicals made in its breakdown interfere with cellular machinery, so it can be used as an antiseptic to kill bacteria. It does also kill living skin cells, but if not used repeatedly can be used to efficiently kill bacteria in a wound, before allowing healthy cells to grow back.

Waste-water treatment processes to remove organic impurities.

Crime scene blood detection. H2O2 radicals made as the haem in blood cells catalyses the breakdown of hydrogen peroxide. The radicals can make a glowing molecule (luminol). A crime scene in sprayed with H2O2 and luminol reveals where the blood is, even if it is at very low concentrations. Detectives use a UV light to see the glowing luminol.

Hair bleach (Marilyn Munroe made the “bleach blonde” fashionable). H2O2 and melanin react, to make colourless melanin.

Glow sticks: H2O2 in glass tube, mixes with a chemical outside. Releases energy again as light. Additional dyes make other coloured glow sticks. Glow stick chemistry activity.

The Play-Debref-Replay method of science is a good format for this activity (see the resource) when student groups each have a set of materials.
As a demonstration, group discussion is aligned with what the activity shows each moment. Students can direct the teacher where to place rocks, and try to model other ideas students mention e.g. tsunami, landslide.

To set up activity: Pile the sand up at one end of the tray, and clip the binder clip to the edge of the tray. Set up the siphon system by submerging the weighted end of the tubing in the large jug of water, then pushing the other end of the tubing through the binder clip at the end of the tray, so that the end hangs over the top of the pile of the sand. Use a squeeze bottle with the air expelled to suck on the tubing and remove the air, to get the water flowing. The water flow slowly runs down the slope of sand.
(Another way to set up this activity is to simply allow students to pour water over a pile of sand. As the flow rate is faster, the more subtle erosion patterns will not be seen, but the sand is still washed down the slope demonstrating erosion.)

Ask that the students simply watch the water flow for a while. This will be tricky if they have their own materials - when the water flow has been started, try requiring that the students watch the flow without touching until they receive their first rock to place in its path. Then pass out rocks one by one, for students to place in the path of the water to change its course, or split the river in two.

Actions for the students to try that focus on the water flow (rather than moving sand around):
Can you make the stream split into two?
Can you find the bank of a stream is washing away as the stream takes a new course?
Can you make a waterfall?
If the sand is made of different coloured particles, how do they separate out?
Where is the sand that is washed downstream being deposited?

After 5 or so mins of water flow, the teacher will need to raise the siphon system up, placing a book or block under the jug, to keep the flow rate up, then again after another little while. The activity ends when the water flow stops.

Group discussion of what students found, during the activity if it is a demonstration, or after students have completed the activity:

• The water flow makes channels in the sand. River valleys are formed the same way - the overlying soil, then the underlying rock are worn away by water (as well as ice and wind). Streams and rivers carve out our landscape to make valleys with mountains on either side, though over a much longer period of time than this activity. The process of sediment removal is called erosion.
• Sand is deposited at the edge of the pool of water at the bottom of the sand hill. Sediment is moved where water flow is faster, and deposited where the flow is slower, so wide shallow bays (deltas) are formed where rivers meet the ocean. Show this image of the Horton River delta in the Northwest Territories: https://www.google.ca/maps/@69.9505943,-126.8071953,12934m/data=!3m1!1e3 (showing a classic delta shape: a triangle, and named after the greek letter delta; the old path of the river can also be clearly seen). As sediment builds up on ocean beds it is compressed by further layering and eventually forms sedimentary rocks.
• The water flow can move the small sand particles but not the larger rocks. In the same way, small rock and soil particles are washed down rivers whereas large boulders remain, sometimes creating waterfalls. Students may notice sand particle colours separating as they are deposited - the differently-sized particles are carried and deposited at different rates.
• Changing the direction of the stream by placing rocks in its path models a rockslide or human structures e.g. dams or dykes, which change the path of rivers.
• Water will find a way down a mountainside, whether over, under or around rocks and other obstacles in its path. Flow of water underground forms cave systems. When we block the path of water with a dam, the stored water has energy, that can be converted to electrical energy as it falls over the turbines of a hydroelectric power station.

To include life sciences: streams and rivers bring life-essential water to animals and plants, bring food to animals that feed on aquatic life, move minerals around that are needed by living things, and provide habitats and homes for plants and animals.

Add a couple of teaspoons of salt to a tub of water and stir to make a solution.
Using the home-made wires from the Electric circuits activity, tape one end of each wire to the batter and dip the other end of each wire into the salted solution.
Make sure the wires are not touching (which would make a short circuit that bypasses the salt solution). Watch for bubbles coming from the wires that are in the water (called electrodes).
The salted water allows electricity to pass, and bubbles of gas are produced at each terminal: hydrogen and chlorine. At one electrode hydrogen gas is produced as the H+ ions in water gain an electron from the electrode, join together to form H2 molecules. At the other electrode, chlorine gas is produced as Cl- ions give an electron to the electrode, join together and form Cl2 molecules. The amounts of chlorine are similar to the amount released by a bottle of bleach: too small to be harmful if not contained - do not let students enclose the gas or smell large amounts of it.

This is a good free play activity. See the Play-Debrief-Replay method of teaching in the resource.
Note: please read through about the short circuit possibility (in bold below), and stop students before the battery and wire gets too hot.

Optional: if using homemade wires, make lengths of masking tape the width of the foil, and tape them next to each other to fill one side of the foil. Tear between the strips of tape, to make lengths of foil backed with tape. (See the 'Making home made wires' photos above.)

Show students their materials: battery, bulb, wires and tape.

Show students how to make circuits by taping wires and bulbs to their desk, making sure there is a good connection between the metals of each.
Optional for budding electricians: show students how to use wire cutters to clip bulbs from a holiday light string, strip the ends to expose the wires, then twist the wires together so that there are no single wires sticking out (thin single wires carrying all the current will heat up and possibly cause burns).
(For Ks show them how to build a simple circuit with two wires, a battery and a bulb, and allow all to succeed before adding more components.)

Start free play.
Note: watch for short circuits - if students bridge the ends of the battery with only a wire, there is no resistance in the circuit and more and more current will flow through the wire. This high current will make the wire and the battery heat up. Keep an eye out at all times and stop students from holding a short circuit configuration for more than a few seconds.

Once students have experimented for a while ask them to leave their materials, and gather to discuss what they find.
Discuss electricity concepts as students come up with them (see phenomena below).
Use circuit symbols to draw what the students describe.

Phenomena likely to come up, and terminology for them:
Short circuit When a battery is connected by a wire looping between both ends, with no bulb. The current can flow fast between the ends of the battery, until the wire and the battery gets hot. Do not let short circuits run for very long. (Buildings have circuit breakers to prevent short circuits from starting a fire.)
Lighting the bulb Students will find that they need to make a circle, containing a battery and a bulb to make the bulb light. Discuss that the electrons flow from one end of the battery (the negative) around the circuit and into the other end of the battery (the positive). If there is no circle, there will be no current and the bulb will not light. The incandescent bulb lights because as electrons squeeze through the thin filament inside the bulb, it heats up and gives off light (LED bulbs work differently). Students may experiment with number of batteries and numbers of bulbs. With incandescent bulbs they will light brighter and brighter as more batteries are added (+ end to - end in a row) until they eventually 'blow' (they do not actually shatter).
Blowing a bulb When enough batteries are connected (with the correct + and - orientation) they will blow a bulb (at least 7 batteries for my materials). When there is enough voltage, so much current is flowing through the filament of the bulb that it melts it, therefore breaking the circuit.
Series circuit A series circuit is when the battery and bulbs are all in a line, so that the electrons move through one component then the next. The energy (voltage) from the battery is divided between the bulbs, so the brightness of a bulb will depend on how many batteries and bulbs there are.
Switch Students will find that some bulbs go on and off as they move the wires around. A contact is not secure and so intermittently breaks the circuit. Real switches (e.g. light switches) break a circuit in a more controlled manner.
Parallel circuit When there is more than one path for the current to flow, most simply with two bulbs straddling one battery the energy from the battery splits and goes down both paths, before rejoining and returning to the battery. The brightness of the bulbs should be the same as when there is just one bulb, as each bulb will draw as much current as one alone when they are in parallel (unlike when they are in series).

Help students come up with new experiments to investigate more deeply (suggest students with similar questions work together).
If they have not already changed numbers of batteries and bulbs, encourage them to do so.
If they have not already made different shapes of circuits (series and parallel), encourage them to do so.

Mix the baking soda and vinegar - this may be a familiar reaction to some. It makes bubbles of gas.
Tell students the chemical reaction that produces the gas, or give students molecule models of the starting molecules and they figure out what the products are (tell them one product is water if necessary):
HCO3 (baking soda, or base) + H (vinegar, or acid) -> H2O (water) + CO2 (carbon dioxide gas)

The molecule models can be purchased (see resource), or made from modelling clay and toothpicks.

This chemical reaction is endothermic - it absorbs heat, so feels cold. A temperature change is an indicator that a chemical reaction is happening.

The baking soda and vinegar reaction is the basis of many science activities, including setting off rockets and making food.